Numerous studies have been conducted on soft handling techniques for strawberries to prevent bruising. For instance, packing systems have been developed that grip the peduncle of the strawberry fruit to prevent damage (Miyata, 2003; Konya and Omori, 2010). However, most strawberries for the Japanese market are without a peduncle, since the peduncle may damage other fruits in shipping containers. Hiyoshi et al. (2002) developed a softhandling-gripper for strawberries that employed a shapememory alloy actuator which handled strawberry fruits with weak forces ranging from 0.1 to 0.2 N. When placing a fruit in a shipping tray, however, the finger may damage other fruits if space is lacking. An end-effector, which carries a fruit on its finger without gripping it, has also been developed (Nagata et al., 1997). Although only a small force is applied to the fruit, it is estimated that the endeffector might fail to place the fruits in the shipping tray in the right posture, since the rolling direction of a strawberry fruit tends to be unpredictable. Suction devices have also been developed that suck the calyx side of the fruit to prevent damage (Nagata et al., 2000; Katogi, 2002). All of them have a suction pad with bellows that is pushed onto the calyx to make a seal. The calyx will not be damaged by this process, but the pericarp of the opposite side of the calyx can be bruised by the pushing motion. In short, no technique has yet been developed which handles strawberry fruit in a reliable manner. More recently, a gentle handling technique has been developed for strawberries using a suction device (Hayashi et al., 2011). Their technique is as follows: first, the orientation and position of the fruit is detected using machine vision system; next, the suction cup approaches the target fruit short of the calyx side and suctions the fruit without pushing or damaging it. They reported that the pickup success rate, without bruising, was more than 95%.

On the other hand, a growing range of shipping styles are now required by consumers, distributors, and strawberry processors to achieve better quality and visual appeal in the market. Single-layer packing methods that employ soft sheets with hollows are increasingly popular, because they can reduce damage during transportation and preserve the quality of the fruits (Nakamura et al., 2008).Furthermore, returnable shipping trays can be used by farmers and processors to save money and protect the environment.

In this article, we describe an automatic packing system for strawberries based on the gentle handling technique developed by Hayashi et al. (2011) and evaluated the system. Farmers normally place fruits in harvesting containers during harvesting and then transfer them to the precooling room. Once the low temperatures render the pericarp hard enough to handle, they start the sorting and packing task. Based on the order of these tasks, we aimed to automate

operations such as picking up fruits from the harvesting container, grading them by size, and methodically packing them. After we had constructed an automatic packing system, we conducted performance tests in a strawberry production area. The objectives of this article are to propose the automatic packing system for strawberries, and to analyze the performance of the automatic system from points of the working speed, the task success rate, the packed fruit posture in shipping trays,and the accuracy of grading.

MATERIALS AND METHODS SYSTEM COMPONENTS

The automatic packing system consists of a packing unit and a supply unit (fig. 1). The supply unit picks up strawberries from the harvesting container. The fruit is then placed on a conveyer and transported to the packing unit. The packing unit grades the fruit according to its size using machine vision system and locates the orientation and the position of each one. Using this geometric information, the unit picks it up and methodically puts it in a shipping tray. Although these two units are controlled by one PC, each unit operates independently. Only the fruit conveyer, which conveys fruits from the supply unit to the packing unit, is affected by the motion status of both units: the conveyer stops when the supply unit puts the fruit on it, or when the packing unit picks up the conveyed fruit.